The present invention generally relates to the field of compression and de-compression of video data transferred via lines having narrow band-width (such as conventional telephone lines). More specifically the present invention relates to a method for transferring live video signals from a video camera to a remote video-displayer, through a conventional telephone line, wherein the said method is especially useful for a fixed camera located at a predetermined location (such as security camera) for monitoring a constant zone, thus having a substantially constant picture background.
The present invention further relates to a system operating by the said method, including a video camera and a video displayer for an interconnection via a conventional telephone line.
In most areas of technology, there is a conflict between well developed technologies (which provide new qualities) and the existing out-of-date infrastructure. The old existing infrastructures delay (or inhibit) the implementation of new technologies since new technologies often require infrastructures of advanced qualities.
Many years ago, when telephone systems were just developed, nobody could predict that the same infrastructure of wiring and relay equipment will be utilized for transferring the surprising volume of electronic data as in these days (data which most of it has nothing with the original xe2x80x9ctelephonexe2x80x9d idea).
The voice-wave vibration range for human ear is between twenty and twenty-thousands Hertz. Accordingly, the required bandwidth of a telephone line is twenty kilohertz. Thus, most of the existing telephone infrastructures cannot be relied for transferring a wider bandwidth data.
However, since a telephone line is commonly the most available connection between two remote locations, efforts are constantly made for adapting wide-bandwidth communication systems to communicate through telephone lines. One example for such a system is a video communication system. The constantly decreased prices of electronic equipment can make video communication systems become very popular, provided that a conventional telephone line will satisfy the wiring requirement between the communicate remote locations. Therefore, many video communication systems using conventional telephone line were developed, all try to prevail the disparity between the video bandwidth requirements and the conventional telephone line bandwidth.
For example, a modest non-colored video picture having a resolution of 354xc3x97288 pixels each having 256 gray tone possibilities, may require a max. bandwidth of 20,340,400 hertz for transferring pictures in a rate of 25 Hz. This rate is as 1,000 times much as a conventional telephone line may provide. Usually the solution for this problem is a combination of three different things; (a) data compression; (b) reducing the rate of picture per second; and (c) reducing the picture resolution. A video picture having the same resolution mentioned above, may be transferred via a telephone line in a rate of ⅓ Hz (i.e. only one picture every three seconds) after having a 90% data compression. The data compression is effective only on average. Radical changes between successive pictures (i.e. of a fast motion), cause a reduction in the compression possibilities, resulting in daubed pictures.
The present invention comply with the above mentioned problem, and provide a new method (and a system using the method), for transferring video pictures via conventional telephone lines. The said method and system, are especially useful for video pictures taken by stationary video cameras (i.e. security cameras).
The present invention relates to a method for transferring live video signals from a video camera of a local system to a remote video-display system via low-bandwidth communication lines. The present invention further relates to a system especially useful for transferring live video data through low-bandwidth communication lines according to the method.
The method of the present invention is comprised of;
(a) acquiring the analog data of an initial-picture by a video camera of a local system; digitizing the said analog data into digital values each presents visual information of one definite picture pixel; grouping the pixels"" digital values data into a plurality of data-blocks each contains data of one particular picture-region associated to its respective location in the picture by a particular address code wherein each picture-region consists of a few neighboring video-pixels taken from at least four neighboring video rows; storing each data-block in a memory means of the local system and successively transferring it with its address code information to a remote video-display system;
(b) storing the transferred data of the initial-picture in memory means of the remote video-display system and converting the said data to a video-picture displayed on a screen of the video-display system;
(c) acquiring successive video pictures by the video camera, digitizing the analog data of each picture into digital values each presents visual information of one definite picture pixel; grouping the pixels"" digital values data into a plurality of data-blocks having the same structure and the same respective addresses as the analogous data-blocks of the initial-picture, subtracting each pixel""s value of a successive picture from the analogous pixel""s value of the initial picture, summing the pixels subtraction results of each block into a single value representing a significance-weight of the respective block, compressing data of blocks having significance-weight value greater than a predetermined threshold-value and transferring this compressed data followed by the respective block addresses to the remote video-display system;
(d) decompressing the said transferred data received by the remote video-display system and refreshing the relevant picture regions of the displayed video picture according to the newly received data.
According to the present invention, the said threshold-value used in step (c) may be a fixed predetermined value, but preferably it is a dynamic value determined automatically as a function of one of the following (or a combination thereof): A) The previous amount of data-blocks having significance-weight greater than the previous threshold value, thus allow optimizing the picture resolution according to the rhythmus of changes in the picture; B) The actual data transfer capacity of the communication line in use.
According to the present invention the threshold value may be also determined considering a preferred picture-refresh rate electrically pointed-out through the communication line by a user of the remote video-display system. This user""s pointing-out may be used directly to determine a threshold value, or according to another variation of the method considerably involved in one of the said A and B options.
Preferably, the step (c) of the method is further comprising the function of compressing and transferring to the remote video-display system data of blocks neighboring to data-blocks having a significance-weight greater than the threshold value (although the neighboring data-blocks themselves have insufficient significance-weight values). The use of this function prevents xe2x80x9cdisappearingxe2x80x9d of small details of the picture such as the extremities of a person in motion (that the picture regions in which they are included may have insufficient significance-weight values). According to one variation of the method of the present invention, this function executed on all the said neighboring data-blocks, without distinction. According to another variation of the method of the present invention, the said function is executed only on those of the said data-blocks having a significance-weight value greater than a lenient secondary threshold value.
According to the method of the present invention, the data compressed and transferred to the remote video-display system is preferably the original digitized picture data (i.e. not the differential data between a current picture and a previous one). In contrast of methods in which a broad picture data is selected to be transferred and the differential data between successive pictures is well compressed, in the method of the present invention the original data of blocks (which significantly differs from the data of respective blocks in the initial picture and thus) selected to be transferred is compressed better. The use of the original data saves calculation resources in both the camera system and the remote video-display system since the only calculation has to be made either for transmitting the video data or for retrieving it is the compression and de-compression calculations.
According to the method of the present invention, preferably each data-block includes the data of a square picture-region holding 64 (8xc3x978) pixels.
The system for transferring live video data through low-bandwidth communication lines according to the present invention is comprising a video-camera system and a video-display system, wherein the video camera system is comprised of a video camera, a variable micro-processor-controlled low-pass filter, an analog-to-digital video-data converter, a digital signal processor, a logical unit, memory means, a programmable address-manager counter, and a communication buffering unit (Modem), wherein video analog data flows from the camera to the variable low-pass filter, converted by the digital-to-analog converter into successively flowing digital values each presents visual information of one definite picture pixel, and the successive digital values are distributed by an addressing sequence of the programmable address-manager counter to a fixed-interval storage addresses of the memory means, thus performing data-blocks respective to picture regions, and wherein in the said logical unit pixels"" visual information digital values of an initial picture are stored in the memory and pixels"" visual information digital values of successive pictures are subtracted respectively from those of the initial picture, the subtraction results of each data-block are summed into a significance-weight value, compared with a predetermined threshold-value, and data of blocks having significance-weight value greater than the threshold value is being compressed by the signal processor and transferred followed by respective address codes through the telephone line to the remote video-display system, de-compressed and displayed.
According to another embodiment of the video-camera system, video analog data flows from the camera to the variable low-pass filter, converted by the digital-to-analog converter into successively flowing digital values each presents visual information of one definite picture pixel, and the successive digital values are being stored successively in the memory means, than being collected from a fixed-interval storage addresses of the memory means by an addressing sequence of the programmable address-manager counter, thus reading the data is made in blocks respective to picture regions. The process now proceeds as described in the first mentioned embodiment.